National Parks Week 2012 is April 21 to 29, and the National Park Service is celebrating by granting free admission to all 397 national parks.

This year, MapQuest launched a web-based guide to national parks to coincide with the week-long celebration of the United States' natural and cultural wonders. The guide currently includes overviews of 58 major destinations, plus information on popular activities, wildlife and park history. Select park entries also include eye-catching video featuring commentary by park rangers (such as the one about Yellowstone featured below), and the panoramic photography of QT Luong.

Luong, a preeminent landscape photographer with a career spanning more than 25 years, uses his camera to "celebrate the splendor and variety of the natural and human heritage," according to his website. Once an "avid mountaineer and climber," Luong has photographed every single national park.

Scroll down to browse some of Luong's most breathtaking panoramas.

The first national park, Yellowstone, was founded before the United States had seen its hundredth birthday. In the face of unchecked 19th century capitalism, which sought to exploit resources with little regard for the environment, a nascent conservation movement led by naturalists like John Muir led the charge to preserve and protect America's natural wonders.

The movement gained momentum into the 20th century, and more parks were established. Philanthropists like John D. Rockefeller, Jr., and other private citizens took up the cause. During the Great Depression, the Civilian Conservation Corps built improvements to the park system's infrastructure, employing 2.5 million young men during its nine-year existence.

In 2011, a looming government shutdown threatened to close national parks and other units managed by the National Park Service, which is an agency of the United States Department of the Interior. The potential shutdown, which was ultimately averted, sprung from a budgetary face-off between the Obama White House and congressional Republicans.

MapQuest is owned by AOL, Inc., which also owns The Huffington Post.

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